This invention relates generally to an apparatus handling a continuous web of paper or like material such as, typically, a web-fed rotary printing press. More specifically, the invention deals with how to preclude, in a rotary printing press or the like, the curling of the web from being held under tension against such relatively small-diameter, web-tensioning members as tension rollers and turnbars for an extended period of time when the machine is out of operation.
As a typical application of the instant invention, let us consider the postprinting station in a web-fed rotary printing press where the printed web is slit longitudinally into a pair of halves and where the web halves are subsequently placed one upon the other. The web is held taut between pairs of nip rollers as it travels along the predefined path through the postprinting station. Conventionally, the web has been held tightly against guide rollers, tension rollers, and turnbars regardless of whether the press is in or out of operation. Left tightened against such members, particularly those of relatively small diameters, for an extended period of time, the web easily develop semipermanent curls.
The curling web has caused some serious inconveniences in subsequent processing thereof. For instance, when the superposed web halves are cut transversely into individual sheets, they have tended to warp while or after being cut, jamming the cutter in the worst case. Furthermore the warping sheets have often impeded such additional postprinting operations as folding, pressing, and delivery, again possibly resulting in jamming or in the wrinkling of the products.
A so-called "decurler" has been known and used for removing the curl from a continuous web or strip of paper that has been kept in roll form, by running the web. The web that has curled from being kept in roll form does so in one direction only, but the web curls indefinitely in both directions in a rotary printing press. Some of such web curls might therefore grow even worse should the web be rubbed only in one way.
There are additional objections to curl removal by rubbing. The forcible rubbing of paper can damage its surface and create large volumes of fibrous dust. Such dust not only deteriorates the quality of the printings but pollutes the working atmosphere.